Shaped charge unit body and method of making same



Feb. e, 1968 A. M. FRANKS ETAL 3,367,282

SHAPED CHARGE UNIT BODY AND METHOD OF MAKING SAME Filed July 12, 1965 United States Patent Ofitice 3,367,282 SHAPED CHARGE UNIT BGDY AND METHOD OF MAKING SAME Archie M. Franks and Harrold D. Owen, Fort Worth, %ex., assignors to Gearhart-Owen, Inc., Fort Worth,

Filed July 12, 1965, Ser. No. 471,238 6 Claims. (Cl. 102-24) Our invention relates in general to well perforating apparatus, especially to perforating apparatus of the expendable jet, or shaped charge type. In particular, our invention relates to improved blasting cord (often known to the trade as Primacord) retaining means for shaped charge unit bodies, and to methods for constructing same.

After completion of the drilling of a well, it is customary to perforate the casing (and the cement which surrounds the casing) in several places adjacent the production zone. One of the most common perforating apparatus is the so-called expendable jet or shaped charge type. Since it is desirable to utilize a number of perforations, individual shaped charge units are arranged in a group, being secured to each other in one of a variety of well known manners to make up a shaped charge gun. The shaped charge units are normally electrically actuated from the surface of the ground via conductor means, a detonator, and blasting cord. The Primacord extends from the detonator to each unit body so that a sequential firing results.

Commonly, each charge unit body is fabricated of materials such as cast aluminum, which have a fluid impervious outer skin and a pervious inner region. Cast aluminum, and other metals which are molded while hot, have a fluid pervious inner region since porosity is a common characteristic of the casting process. The fluid impervious outer skin results from the reaction of the cold die or mold as it engages the hot metal. This impervious skin prevents the drilling fluid with its accompanying moisture from entering the shaped charge unit via the pervious inner region and causing a .misflre of the shaped charge. If the outer skin is broken, a weeping condition may occur in the inner region; that is, moisture may weep through the inner region and dampen the charge. The prior art devices with which We are familiar have blasting cord retainers attached to each unit body in a manner such that the impervious outer skin of either the unit body or the retainer is broken during the manufacture or the assembly of these parts. Moreover, even when the blasting cord retainer is formed integrally with the unit body, a machining operation is required, and this operation of course ruptures the outer skin.

Although cast pieces have inner as well as an outer impervious skin, it is only the outer skin that effectively prevents weeping. Fluid pressures in well bores commonly reach 10,000 psi or greater. Such pressures will not rupture the outer skin since this skin is well supported by the inner regions of the shaped charged unit body. The inner skin, however, is essentially unsupported and will easily rupture under the influence of great pressure differentials (the pressure inside the hollow body is approximately atmospheric). Thus, it is highly desirable that the outer skin be undamaged since the inner skin will not prevent moisture from reaching the shaped charge.

Prior art blasting cord retainers frequently have sharp corners or edges which increase the possibility of damaging the blasting cord during or after assembly in the retainer. It is apparent that if a blasting cord has a damaged surface, moisture may enter therethrough and frequently cause a misfire. Therefore, it is beneficial for blasting cord retainers to have rounded corners and edges so as not to damage the blasting cord.

3,367,282 Patented Feb. 6, 1968 The general object of our invention is to provide an improved blasting cord retaining means for well perforator shaped charge units and a method for making same.

Another object is to provide a method for constructing a blasting cord retainer on a shaped charge unit body having a fluid pervious inner region and an impervious skin without damaging the surfaces of the body.

Another object is to provide a blasting cord retainer formed by a method which does not produce sharp corners or edges on the retainer.

These and other objects are effected by our invention as will be apparent from the following description taken in accordance with the accompanying drawing, forming a part of this application, in which:

FIG. 1 is a perspective view of a typical shaped charge unit, including a blasting cord retainer constructed in accordance with the principles of our invention;

FIG. 2 is an elevational view of the rear of the shaped charge unit of FIG. 1;

FIG. 3 is a fragmentary elevational view of the retainer portion of the shaped charge unit of FIG. 1, showing an intermediate structure prior to ultimate configuration thereof; and

FIG. 4 is a view, similar to FIG. 3, showing the ultimate configuration of the blasting cord retainer.

Referring now to the drawing, FIG. 1 illustrates a typical shaped charge unit 11 which includes a charge unit body 13, a charge unit body cap 15, and upper and lower coupling links (shown as fragments) designated 17, 19 respectively.

The term charge unit body refers to that portion of the shaped charge unit which supports the blasting cord retainer. This is normally the part designated by numeral 11, but in some instances the cap 15 supports the retainer and thus it becomes the charge unit body. However, the cap end of the charge unit 11 is normally referred to as the front end and the opposite end, which is shown clearly in FIG. 1, as the rear end. The rear end of the charge unit body 13 has a frusto-conical end wall 21. The ribs 23, 25 are integrally molded or cast on charge unit body 13 and are disposed so that their mutually opposed substantially parallel inner walls 30, 32 diverge at a slight angle with respect to the vertical axis of the charge unit body 13, as shown in FIG. 3. It will be noticed also from it merges with the end wall 21. Each rib'23, 25 preftapered shape in transverse cross section; that is, each rib is slightly thinner at the top than at the bottom where it merges with the end wall 21. Each ribs 23, 25 preferably has an integrally formed, oval-shaped protrusion or boss designated respectively 27 or 29, which protrudes outwardly from the top of the rib and slightly inwardly therefrom. The opposing side walls 31,. 33 (see FIG. 3) of the bosses 27, 29 are substantially parallel.

Initially, the hoses 27, 29 are disposed as shown in FIG. 3, and because the side walls 31, 33 are substantially parallel, they will not retain the blasting cord 35 therebetween. However, we have found that the ribs 23, 25 and bosses 27, 29 may be formed to a configuration that will effectively retain the blasting cord. This is accomplished by deforming the bosses 27, 29 by means of a suitable tool, generally a die.

One operating end of the forming instrument 37 of FIG. 3 is approximately as long as the bosses and approximately as wide as the distance between the outside walls of the ribs 23, 25. In the end thereof is a forming channel 39 which has side walls 41, 43 that merge into a substantially flat surface by means of fillets 47, 49. FIG. 3 shows the ribs 23, 25 in the initial stage, prior to engagement with the forming instrument 37.

To form a blasting cord retainer, the forming instrument 3'7 is positioned as shown in FIG. 3, with the side walls 41, 43 in contact with the outer top edge of the ribs 23, 25. The forming instrument 37 may now be forced downward relative to the ribs 23, 25 in any suitable manner. One such manner is to actuate the forming instrument by means of an ordinary punch press. Another manner is to actuate the forming instrument in a hydraulically operated press mechanism.

In'a typical embodiment, the forming instrument 37 moves downward about inch. While the forming instrument is moving downward through this distance, two principal effects are produced: (1) the forming tool sidewalls 41, 43 engage the oppositely facing outer walls 22, 24 of the ribs and urge the side walls 31, 33 of the bosses 27, 29 inwardly toward each other, and (2) the bottom surface 45 of said instrument engages the protruding top surfaces of the bosses and forces the ma-. terial thereof downwardly and inwardly. Thus, the net effect of these reactions is to change the cross sectional shape of the groove 34 between the walls 31, 33 from its initial rectangular shape (see FIG. 3) to a generally trapezoidal shape, as shown in FIG. 4. Furthermore, it should be noted that the top and bottom longitudinal edges 44, 46 of the groove 34, which are rounded initially (see FIG. 3), remain rounded during and after the deforming of the protruding top bossing material (see FIG. 4). In a typical instance the resulting trapezoidal shaped. groove will be about 5 inch narrower at the top than at the bottom.

While in a preferred embodiment the bosses 27, 29 are shown as having an oval-shape, it should be understood that other shapes may be used if preferred.

In the preferred embodiment shown in FIG. 3, the ribs 23, 25 have tapering walls 30, 32 and the channel 29 of the forming instrument 37 has substantially parallel walls 41, 43. It should be understood, however, that the walls 30, 32 of the ribs may, if preferred, be substantially parallel and the walls 41, 43 of the channel may converge or taper toward the bottom surface 45. As mentioned previously, one of the desired effects of using the forming instrument is to cause the ribs to converge slightly toward each other at the upper edges thereof, and this may be achieved with any appropriate instrument of any suitable shape.

From the foregoing, it will be apparent that our method of forming a satisfactory blasting cord retainer is remarkably simple, economical and effective.

Another advantage of our invention is that the skin of the blasting cord holding and retaing groove is not broken. Consequently, a weeping condition in the charge body interior is avoided. Such a weeping condition generally obtains as a result of breaking the skin of the charge body which exposes the relatively porous interior thereof. In such an event, moisture weeps through the skin into the inside of the body and frequently causes a misfiring of the unit. Such weeping, of course, is particularly critical in the ignition end of the charge unit, i.e. at the area where the blasing cord engages the unit.

Another advantage of our method is that sharp corners or edges are eliminated, thus reducing the possibility of chafing the blasting cord. It is recognized that prior art procedures do tend to leave sharp corners and edges which chafe the blasting cord to such an extent that moisture enters the blasting cord. This condition frequently results in a misfiring of the charge unit. But, as mentioned previously, the method of the present invention does not destroy the initially rounded corners and edges, and, consequently, there is no chafing of the blasting cord or misfiring of the charge unit.

Another advantage of our invention is that our method of forming the blasting cord retaining groove produces adequate bearing surfaces on the top edge of the bosses.

Some prior art arrangements do not provide a sufficient bearing surface at this location, and consequently, the inevitable rubbing of the charge body against the wall of the tubing, casing, or bore hole produces a rapid wearing of the groove wall material. Hence, the blasting cord is soon exposed and chafed. As mentioned previously, when the biasing cord is chafed, moisture enters therein and a misfiring frequently results.

While the method of the present invention is directed primarily to problems encountered with cast aluminum charge bodies, the principles of our invention are, of course, applicable to charge bodies made of other suitable materials. The method is particularly applicable to other materials which when cast or molded in a heated condition have an outer skin that is imprevious to moisture, but which have a relatively porous interior structure; such other suitable materials, of course, are known to those skilled in the art.

The foregoing disclosure and the showings made in the drawing are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense.

We claim:

1. The method of forming a Primacord retainer on a shaped charge unit body, said method comprising the steps of:

(a) die-casting an aluminum shaped charge unit body which integrally includes a pair of spaced apart ribs extending outwardly therefrom, said ribs having mutually opposed substantially parallel walls and oppositely facing outer walls which mutually converge; and then (b) deforming said ribs to cause the mutually opposed walls thereof to converge toward each other at least near their outer extremities, with the deforming of said ribs being efiected by a forming tool having a channel therein the walls of which engage said outer walls to exert a lateral deformative force on said ribs as said forming tool is forced downwardly against said ribs.

2. The invention as defined by claim 1 wherein said ribs have protrusions with mutually opposed surfaces which extend inwardly from the ribs and upper surfaces which extend outwardly beyond the ribs, and said forming tool engages the outermost portions of the protrusions and exerts a downward deformative force against them in addition to said lateral deformative force.

3. The method of forming a blasting cord retainer on a shaped charge unit body, said method comprising the steps of:

(a) molding while in a heated condition a metallic shaped charge unit body which integrally includes a pair of spaced apart ribs extending outwardly therefrom, said ribs having protrusions with mutually opposed surfaces which extend inwardly from the ribs and upper surfaces which protrude outwardly beyond the ribs; and then (b) deforming at least the protrusions of said ribs to cause the opposed surfaces of the protrusions to converge toward each other at least near their outer extremities.

4. The method of forming a blasting cord retainer on a shaped charge unit body, said method comprising the steps of:

(a) die-casting an aluminum shaped charge unit body which integrally includes a pair of spaced apart ribs extending outwardly therefrom, said ribs having protrusions with mutually opposed surfaces which extend inwardly from the ribs and upper surfaces which extend outwardly beyond the ribs; and then (b) deforming at least the protrusions of said ribs to cause the mutually opposed surfaces of the protrusions to converge toward each other at least near their outer extremities.

5. In an article of manufacture which is a shaped charge unit body of a well perforator, said body being formed of a material having a fluid pervious inner region, a fluid impervious skin, and a pair of spaced apart ribs which extend 6 integrally and outwardly from the body, the improvement References Cited comprising a pair of protrusions formed integrally on UNITED STATES PATENTS said ribs, sa1d protrusions having opposed surfaces which 2 extend inwardly from the ribs, and upper surfaces which gififigiiii 2 protrude outwardly beyond the ribs, said protrusions being 5 readily deformable to facilitate the subsequent formation 3048101 8/1962 Lebourg of a Primacord retainer.

6. The invention as defined by claim 5 wherein said BENJAMIN BORCHELT Pr'mary Examiner material is die-cast aluminum. V. R. PENDEGRASS, Assistant Examiner. 

1. THE METHOD OF FORMING A PRIMACORD RETAINER ON A SHAPED CHARGE UNIT BODY, SAID METHOD COMPRISING THE STEPS OF: (A) DIE-CASTING AN ALUMINUM SHAPED CHARGE UNIT BODY WHICH INTEGRALLY INCLUDES A PAIR OF SPACED APART RIBS EXTENDING OUTWARDLY THEREFROM, SAID RIBS HAVING MUTUALLY OPPOSED SUBSTANTIALLY PARLLEL WALLS AND OPPOSITELY FACING OUTER WALLS WHICH MUTUALLY CONVERGE; AND THEN (B) DEFORMING SAID RIBS TO CAUSE THE MUTUALLY OPPOSED WALLS THEREOF TO CONVERGE TOWARD EACH OTHER AT LEAST NEAR THEIR OUTER EXTREMITIES, WITH THE DEFORMING OF SAID RIBS BEING EFFECTED BY A FORMING TOOL HAVING A CHANNEL THEREIN THE WALLS OF WHICH ENGAGE SAID OUTER WALLS TO EXERT A LATERAL DEFORMATIVE FORCE ON SAID RIBS AS SAID FORMING TOOL IS FORCED DOWNWARDLY AGAINST SAID RIBS. 